1. Field of the Invention
The present invention relates generally to a semiconductor structure and process thereof, and more specifically, to a semiconductor structure having a fluoride metal layer, and process thereof.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices like metal-oxide-semiconductors (MOS). With the trend towards scaling down the size of semiconductor devices, conventional poly-silicon gates face problems, such as inferior performance due to boron penetration and unavoidable depletion effect. This increases the equivalent thickness of the gate dielectric layer, reduces the gate capacitance, and decreases the driving force of the devices. Therefore, work function metals that are suitable to serve as high-K gate dielectric layers are used to replace the conventional poly-silicon gate to be the control electrode.
As semiconductor technologies are miniaturized to the nanometer scale, work function metal gate structures are close to their physical and electrical limitations, giving rise to problems of electrical unreliability of the gate structures, such as degraded NBTI values (negative bias temperature instability). For a complementary metal-oxide semiconductor (CMOS), dual work function metal gates need to be paired with an NMOS component and a PMOS component; integrated technologies and process controls of components are therefore more complicated, and the process efficiency restrained. Thus, the improvement of the electrical performances of the gate structures of PMOS or NMOS transistors is a big challenge to overcome, by, for example, improving the work function value of the gate structures.